Fuse link



E. F. BOOTHE Feb. 22, 1938.

FUSE LINK Filed May 25, 1936 5 aww.. w A 4.

Patented Feb. 22, 1938 UNITED STATES PATENT OFFICE FUSE LINK Eugene F. Boothe, St. Louis, Mo.,A assigner to James R. Kearney Corporation, St. Louis, Mo., a corporation of Missouri Application May 25, 1936, Serial No. 81,636

4 Claims. (Cl. 20D-117) This invention relates generally to fuse links, termined that an unstressed fuse wire which is and more specifically to fuse links of the tension intended tc become ruptured upon passage theretype provided with strain-absorbing means for through of, say, three-fourths of an ampere, when relieving the fusible elements of the link of tensile held under mechanical tension of the order prostrains which would be otherwise imposed thereduced by spring means found in the usual .types of on, the predominant object of the invention being protective apparatus, is ruptured by currents of a to provide a fuse link with strain-relieving means magnitude substantially less than the figure of such construction and arrangement that, while specified. the unruptured fuse link is provided with great The purpose of this invention, therefore, is to in tensile strength, quick separation of parts of the provide a fuse link construction which will not 10 fuse link on rupture of the fusible element therebe harmfully affected by the application thereto of is not unduly interfered with by the strainof relatively high mechanical forces by relieving labsorbing means. in an improved manner the fusible element of Another extremely important object of the inthe improved fuse link structure of the forces l5 vention is to provide a fuse link which is so conpredueed by the tensioning means, and Whieh iS 15 structed and arranged that during a switching or less likely to open during passage of a surge of lightning surge of current the improved fuse link current due to switching 0r lightning than Were is less likely to open than the conventional fuse fuse links not constructed in accordance with link not constructed and arranged in accordance this invention.

90 with this invention. This results from the fact Fig. 1 is a VieW, partly in Vertical SeCtiOn and 20 that an arcing gap is provided in the fuse 1ink partly in side elevation, of a fuse cartridge havstructure between the Strain-absorbing means ing the improved fuse link associated therewith. and an adjacent portion of the fuse link structure, Fig. 2 is a fragmentary View, partly in Vertical and when the surge passesr through the fusible section and partly in elevation, of a portion of the 5 element 0f the fuse link Structure there is a, volt- Structure illustrated ll Fig. l, but Viewing Same n, age drop across the arcing gap sufficient to cause frena a different angleb the gap to break down and by-pass a portion of In the drawing, Whel'ein is ShOWn fOr the D111- the current over the gap. kThe time duration in- Pese 0f illustration, merely, One embodiment of volved is so small that the strain-absorbing means the inVentiOn, A designates a fuse Cartridge adja- 30 is not burned in 13W() by the lay-passed eurent,y Celli) t0 the IOWBI end Of WhlCh a, terminal memim and hence the fuse link is not damaged by the bei B is ilXed, Seid terminal member B being Surge current, adapted to aid in electrically associating the fuse Fuse links of the type referred to above 0rcartridge A with a switch apparatus (not shown). dinarily are adapted to be hel-d under mechan- At its upper end the fuse Cartridge A has aSSO- ical tension produced either by spring means Cieted With it en adapter C Which COInDrlses a' Q@ .which form parts of the fuse link structures, or Snert tubular Dertien Cn that iS eXtended dOWnparts of the protective apparatus with which the Werdly into the tube A Of the fuse Cartridge A, fuse links are associated, the purpose being to end en Outstanding annular ilenge Cb Which 00ncreate a wide gap between the severed ends of the tette With the tOD face 0f Said tube- 0 fusible element of the fuse link after the same The iInDrOVed fuse link includes e entaet head has become ruptured by passage of abnormal ourl which is xedly located at the outer end of a rent, and to quickly extinguish any are attendstrip 2 of conducting material which serves as a ing the blowing of the fusible nement by causing terminal member of the fuse link, said contact the ruptured ends thereof to fly apart under the heed being arranged in COnteCt With the t0n faee action of the spring tension. of the flange Cb of the adapter C, and said strip 2 4- A heretofore prevailing difficulty inherent in being' eXtended ldOVVnWardly inte the tube A Of tension fuse links, particularly those of low or the cartridge A- Extended upwardly thrOugh the fractional ampere current carrying capacity, recartridge tube A' is an electrical conductor 3,

sulted from the tendency of the fusible element which serves as a terminal element of the fuse to become severed by reason of the mechanical link, the end 3 of said conductor which is located 50 forces applied thereto, or if not actually severed within the tube A being spaced a considerable the application of such forces to the fusible eledistance from the inner or lower end of the strip ment for a long period of time resulted in altera* 2. The opposite end portion of the conductor 3 tion of 'the operating characteristics, or rating, is turned about the lower end of the fuse cartridge ofthe fuse link. In other words, it has been deand is extended upwardly with respect thereto, 55

as indicated at 3iL in Fig. l, said upwardly extended portion of said conductor being mechanically and electrically clamped to the terminal member B of the fuse cartridge through the instrumentality of a suitable clamping screw D.

The strip 2 and the conductor 3 are connected together by connecting means which includes a strain wire 4 that is extended thr-ough apertures 5 formed through a pair of blocks 5 formed of fiber or other suitable electrical insulating material. These blocks 5 are secured to the strip 2 at opposite side faces thereof by means of a rivet 6 or other suitable fastening means which passes through apertures formed through the blocks 5 and the strip 2 (see Fig. l). The portion le of the strain wire which extends through the apertures 5 of the blocks 5 may be described as a bridge portion, and extended from the opposite ends of this bridge portion are substantially parallel strain wire portions 4b, end p-ortions of which are arranged parallel and in Contact with the adjacent end portion of the conductor 3. The end portions of the strain wire portions 4b are secured to the conductor 3 by a sleeve l formed of conducting material which closely embraces the end portion of the conductor and the portions of the strain wire portions lib which contact therewith. As shown in Figs. l and 2, the sleeve l, which by preference is formed of suitable metal, is flattened as is the end portion of the conductor 3, and therefore the end portions of the strain wire portions 4b are very securely clamped to the conductor 3 by said flattened sleeve i. In order to eliminate any chance that the tensional strains to which the strain wire 4 is subjected may result in the strain wire portions [ib being pulled from between the sleeve 'l and the conductor 3, said portions 4b are preferably bent double, as shown by dotted lines in Fig. 2, and also at bent ends 4C of said strain wire portions 4b, which extend slightly outside of the sleeve l, soldered joints produced which iirmly secure the strain` wire and the sleeve 'l together.

With regard to the strain wire il, it is of exe treme importance to note that a gap G (see Fig. l) is present between the strain wire and the strip 2, and this gap takes the strain wire out of direct electrical connection with the strip E and under normal conditions prevents the strain wire from being a direct part of an electrical circuit of which the fuse link forms a part.

Secured by solder or otherwise at one the strip 2 and by solder or otherwise at the opposite end to the sleeve l is the fusible element 8 of the fuse link. As shown to the best advantage in Fig. 2, the fusible element 8 is out of direct electrical connection with the strain wire d.

Extended downwardly from the strip 2 is an expulsion tube 9 formed of electrical insulating material which embraces the extreme lower porn tion of the strip il, the lower ends of the blocks 5, the strain wire 4, the sleeve l, a portion of the conductor 3, and a large part of the fusible element 8. The lower portion 2 of the strip 2 which extends into the expulsion tube is of reduced width, whereby said strip is provided with shoulders 2St which contact with the upper edge of the expulsion tube. Extended upwardly into the expulsion tube 9 from a point a considerable distance below the lower edge of said expulsion tube is an elongated tubular element i0, which at its lower end is provided with an outstanding, annular flange ll, and an expansible coil spring l2 is interposed under compression between said annular flange of the tubular element l0 and the lower end to edge of the expulsion tube 9. A button I3 is secured to the conductor 3, and this button holds the tubular element in its elevated position so that the coil spring l2 is maintained in compression.

In the use of the improved fuse link disclosed herein, the strain wire 4 is not in direct electrical contact with the strip 2 because of the presence of the gap G which separates the bridge portion 4a of said strain wire from said strip, hence all electrical current conducted by the fuse link under normal operating conditions must flow through the fusible element S. When a fault occurs in the line protected by the improved fuse link, the fusible element 8 melts and thereafter the current flows through the strain wire 4, said current passing from the end of the strip 2 to said strain wire in the form of an arc. The arc thus produced breaks the strain wire at the bridge por tion la thereof, allowing the separated ends of said bridge portion to be pulled out of the apertures 5' of the blocks 5 by the associated switch mechanism or by the coil spring l2, and thus permit the fuse link to separate. The importance of the gap- G resides in the fact that a small frac tion of an ampere through an arc will break a strain wire of the required strength, whereas, if the strain wire were continuous, several amperes would be required in order to melt the strain wire and break the circuit.

[i further important advantage of the gap G is that during a surge of current through the improved fuse link due to switching or lightning, the fuse link is much less likely to open than a fuse link not provided with such a gap. This results from the fact that when the surge passes through the fusible element, for instance, 10,000 amperes in 3 or 4 micro-seconds, there is a Voltage drop across the arcing gap G sufficient to cause the gap to break down and by-pass a portion of this current over the gap, and because the time duration of such lay-passing of current is so small the strain wire is not burned in two and the fuse link is not damaged by the surge of current.

I claim:

l. A fuse link assembly including a pair of spaced terminal members, a fusible element for electrically connecting said terminal members, and connecting means for mechanically connecte ing said terminal members so as to relieve said fusible element of tension applied to the fuse link assembly, said connecting means including a strain wire connected to one of said terminal members and insulating means for connecting said strain wire to the other of said terminals in spaced relation with respect thereto, so as to provide a gap between said strain wire and said terminal, which electrically separates same durnormal operation of the fuse link assembly and over which current passes during abnormal passage of current through the fuse link assembly, said insulating means including a block secured to said terminal member and provided with an aperture through which said strain wire passes so as to provide a portion of the strain wire which is disposed in spaced alinement with the adjacent terminal to produce said gp- 2. A fuse link assembly including a pair of spaced terminal members, a fusible element for electrically connecting said terminal members, and connecting means for mechanically connecting said terminal members so as to relieve said fusible element of tension applied to the fuse link assembly, said connecting means including a strain wire connected to one of said terminal members and insulating means for connecting said strain wire to the other of said terminals in spaced relation with respect thereto, so as to provide a gap between said strain wire and said terminal, which electrically separates same during normal operation of the fuse link assembly and over which current passes during abnormal passage of current through the fuse link assembly, said insulating means including a pair of spaced blocks secured to said terminal member at opposite sides thereof and provided with apertures through which said strain wire passes so as to provide a portion of the strain wire which is disposed in spaced alinement with the adjacent terminal to produce said gap.

3. A fuse link assembly including a pair of spaced terminal members, a fusible element for electrically connecting said terminal members, and connecting means for mechanically connecting said terminal members so as to relieve said fusible element of tension applied to the fuse link assembly, said connecting means including a strain Wire connected to one of said terminal members and insulating means for connecting said strain wire to the other of said terminals in spaced relation with respect thereto, so as to provide a gap between said strain Wire and said terminal, which electrically separates same during normal operation of the fuse link assembly and over which current passes during abnormal passage of current through the fuse link assembly, said insulating means including a pair of spaced blocks secured to said terminal member at opposite sides thereof and provided with apertures through which said strain Wire passes so as to provide a portion of the strain wire which is disposed in spaced alinement with the adjacent terminal to produce said gap, and a sleeve for attaching the strain Wire to the other terminal member.

4. A fuse link assembly including a pair of spaced terminal members, a fusible element for electrically connecting said terminal members, and connecting means for mechanically connecting said terminal members so as to relieve said fusible element of tension applied to the fuse link assembly, said connecting means including a strain wire connected to one of said terminal members and insulating means for connecting said strain Wire to the other of said terminal members in spaced relation with respect thereto, so as to provide a gap between said strain wire and said terminal member which electrically separates same during normal operation of the fuse link assembly and over which current passes during abnormal passage of current through the fuse link assembly, said insulating means being secured to said terminal member and having the strain wire so associated and assembled therewith as to space a portion of the strain Wire from the adjacent terminal member to produce said gap.

EUGENE F. BOOTHE. 

